Merge pull request emscripten-core#4569 from juj/proxy_main_runtime_t…

…hread

Allow user code to proxy functions to be called in the main thread.

Merge pull request emscripten-core#4579 from juj/nanosleep_in_pthreads

Implement nanosleep() in pthreads. Fixes emscripten-core#4578.

Merge pull request emscripten-core#4496 from juj/asmjs_sbrk

asmjs_sbrk

Merge pull request emscripten-core#4497 from juj/deprecate_writeStrin…

…gToMemory

Deprecate writeStringToMemory()